| In the first part of dissertation, we investigate the approaches to exploit multiuser diversity at uplink and downlink transmissions of a cellular system and evaluate their performance. For the downlink transmissions, we study a cellular network with one t-antenna base station and K r-antenna users. With time-varying fading, multiuser diversity is exploited by always allowing the base station to transmit to the user with the best channel. For this network, we investigate the impact of the number of antennas, correlated fading or mobility to the multiuser diversity scheduling. In addition, to study channel state information (CSI) of multiple-input multiple-output (MIMO) channels, we evaluate the correlation coefficient for instantaneous mutual information of the temporally correlated MIMO channels. To exploit the multiuser diversity at the uplink, we propose to use reservation random access schemes such as reservation slotted ALOHA and reservation slotted nonpersistent ISMA. When channel state information is not available to single-antenna users when they contend for channel access to a single-antenna basestation, we find that capture effect inherent in wireless communications can exploit the channel variations and reserve users with favorable channels for data transmission.In the second part of the dissertation, we propose novel interference cancellation schemes to improve the efficiency of RFID tag detection. In a RFID system, readers need to acquire ID information stored in tags via the wireless channel. The binary search algorithm is used to coordinate the transmissions from multiple tags to one reader. In this dissertation, we propose a new approach to use interference cancellation in the binary search algorithm, which achieves time saving of around 50% to read all tags' IDs. In addition, for algorithms with and without interference cancellation, we analyze the reliability of ID detection and obtain analytical results of the average probability of success for ID detection. |
